The present invention relates to the use of homopolymers of propylene or copolymers of propylene with C2-C10-alk-1-enes, which polymers are obtainable by polymerization of the corresponding monomers using metallocene catalysts, for producing moldings, preferably hollow bodies, in particular injection-molded articles.
Plastics, in particular olefin polymers, are processed into moldings using the injection molding technique.
However, such moldings, or the polymers on which they are based, have disadvantages.
Moldings having high transparency, for example made of random copolymers of propylene with other olefins, usually have unsatisfactory stiffness, expressed by the E modulus in accordance with ASTM D882.
On the other hand, moldings having a high stiffness, for example made of homopolymers of propylene, generally have insufficient transparency, measured in accordance with ASTM D1003.
Many of the currently available polyolefins which are employed in injection molding also have unsatisfactory organoleptic properties (unpleasant odor and/or taste of the finished article).
It is an object of the present invention to develop polymers which combine high transparency with, at the same time, good stiffness and which additionally have a low odor and/or taste (good organoleptic properties) and a low proportion of xylene-soluble material, preferably less than 1.5% by weight.
We have found that this object is achieved by the use of homopolymers of propylene or copolymers of propylene with C2-C10-alk-1-enes, which polymers are obtainable by polymerization of the corresponding monomers using metallocene catalysts, for producing moldings and injection-molded articles as defined in the claims.
The propylene polymers according to the present invention are propylene homopolymers or copolymers of propylene and an alk-1-ene or a plurality of alk-1-enes selected from the group consisting of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and 4-methyl-1-pentene, or mixtures of these polymers, where the mixing ratios are not critical. For the purposes of the present invention, copolymers are generally random copolymers.
The propylene homopolymers are essentially isotactic.
The homopolymers of propylene or copolymers of propylene with C2-C10-alk-1-enes, having the above-described composition and structure, are obtained by polymerization of the corresponding monomers using metallocene catalysts. Hereinafter, such propylene polymers are referred to as xe2x80x9cpropylene homopolymers and copolymers according to the present inventionxe2x80x9d.